Silicon oxycarbide environmental barrier coating

ABSTRACT

An article includes a ceramic-based substrate and a barrier layer on the ceramic-based substrate. The barrier layer includes a matrix of barium-magnesium alumino-silicate or SiO2, a dispersion of silicon oxycarbide particles in the matrix, and a dispersion of particles, of the other of barium-magnesium alumino-silicate or SiO2, in the matrix.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.15/110,523, filed on Jul. 8, 2016, which is a national phase entry ofInternational Application No. PCT/US2015010442, filed Jan. 7, 2015,which claims priority to U.S. Provisional Application No. 61/927,101,filed Jan. 14, 2014.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under contract numberN00014-09-C-0201 awarded by the United States Navy. The government hascertain rights in the invention.

BACKGROUND

This disclosure relates to composite articles, such as those used in gasturbine engines.

Components, such as gas turbine engine components, may be subjected tohigh temperatures, corrosive and oxidative conditions, and elevatedstress levels. In order to improve the thermal and/or oxidativestability, the component may include a protective barrier coating.

SUMMARY

An article comprising a ceramic-based substrate according to an exampleof the present disclosure includes a barrier layer on the ceramic-basedsubstrate. The barrier layer includes a matrix of barium-magnesiumalumino-silicate or SiO₂ and a dispersion of silicon oxycarbideparticles in the matrix. The silicon oxycarbide particles have Si, O,and C in a covalently bonded network, and a dispersion of particles, ofthe other of barium-magnesium alumino-silicate or SiO₂, in the matrix.

In a further embodiment of any of the foregoing embodiments, the barrierlayer includes, by volume, 1-30% of the barium-magnesiumalumino-silicate particles.

In a further embodiment of any of the foregoing embodiments, the barrierlayer includes, by volume, 30-94% of the silicon oxycarbide particles.

In a further embodiment of any of the foregoing embodiments, the barrierlayer includes, by volume, 5-40% of the matrix of SiO₂.

In a further embodiment of any of the foregoing embodiments, the barrierlayer includes, by volume, 1-30% of the barium-magnesiumalumino-silicate particles, 5-40% of the matrix of SiO₂, and a balanceof the silicon oxycarbide particles.

In a further embodiment of any of the foregoing embodiments, the barrierlayer includes, by volume, 1-5% of the barium-magnesium alumino-silicateparticles.

A further embodiment of any of the foregoing embodiments includes adistinct intermediate layer between the barrier layer and theceramic-based substrate, the distinct intermediate layer including anintermediate layer matrix of SiO₂ and a dispersion of intermediate layersilicon oxycarbide particles in the intermediate layer matrix.

In a further embodiment of any of the foregoing embodiments, the siliconoxycarbide particles in the barrier layer have an average maximumdimension D1 and the intermediate layer silicon oxycarbide particles inthe distinct intermediate layer have an average maximum dimension D2,and D2 is less than D1.

In a further embodiment of any of the foregoing embodiments, thedistinct intermediate layer includes, by volume, 5-40% of theintermediate layer matrix of SiO₂ and a balance of the dispersion of theintermediate layer silicon oxycarbide particles.

In a further embodiment of any of the foregoing embodiments, the matrixof SiO₂ is continuous.

In a further embodiment of any of the foregoing embodiments, the siliconoxycarbide particles have a composition SiO_(x)M_(z)C_(y), where M is atleast one metal, x<2, y>0 and z<1 and x and z are non-zero.

In a further embodiment of any of the foregoing embodiments, the siliconoxycarbide particles have an average maximum dimension of 1-75micrometers.

A further embodiment of any of the foregoing embodiments includes aceramic-based top coat on the barrier layer.

In a further embodiment of any of the foregoing embodiments, the barrierlayer consists of the matrix of SiO₂, the dispersion of the siliconoxycarbide particles in the matrix, and the dispersion of thebarium-magnesium alumino-silicate particles in the matrix.

A composite material according to an example of the present disclosureincludes a matrix of barium-magnesium alumino-silicate or SiO and adispersion of silicon oxycarbide particles in the matrix. The siliconoxycarbide particles have Si, O, and C in a covalently bonded networkand a dispersion of particles, of the other of barium-magnesiumalumino-silicate or SiO₂, in the matrix.

A further embodiment of any of the foregoing embodiments includes, byvolume, 1-30% of the barium-magnesium alumino-silicate particles, 5-40%of the matrix of SiO₂, and a balance of the silicon oxycarbideparticles.

A further embodiment of any of the foregoing embodiments includes, byvolume, 1-5% of the barium-magnesium alumino-silicate particles.

In a further embodiment of any of the foregoing embodiments, the matrixof SiO₂ is continuous.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the present disclosure willbecome apparent to those skilled in the art from the following detaileddescription. The drawings that accompany the detailed description can bebriefly described as follows.

FIG. 1 illustrates an example article having a barrier layer of acomposite material that includes barium-magnesium alumino-silicateparticles.

FIG. 2 illustrates a network of silicon oxycarbide.

FIG. 3 illustrates another example article having a barrier layer of acomposite material that includes barium-magnesium alumino-silicateparticles.

FIG. 4 illustrates another example article having a barrier layer of acomposite material that includes barium-magnesium alumino-silicateparticles.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a representative portion of an examplearticle 20 that includes a composite material 22 that is used as abarrier layer. The article 20 can be a gas turbine engine component,such as but not limited to, an airfoil, a combustor liner panel, a bladeouter air seal, or other component that would benefit from the examplesherein. In this example, the composite material 22 is used as anenvironmental barrier layer to protect an underlying substrate 24 fromenvironmental conditions, as well as thermal conditions. As will beappreciated, the composite material 22 can be used as a stand-alonebarrier layer, as an outermost/top coat with additional underlyinglayers, or in combination with other coating under- or over-layers, suchas, but not limited to, ceramic-based topcoats.

The composite material 22 includes a matrix of silicon dioxide (SiO₂)26, a dispersion of silicon oxycarbide particles (SiOC) 28 in the matrix26, and a dispersion of barium-magnesium alumino-silicate particles 30(“BMAS particles 30”). In an alternative of any of the examples herein,the matrix can be the barium-magnesium alumino-silicate and thedispersion of particles can be silicon dioxide. The silicon oxycarbideparticles 28 have silicon, oxygen, and carbon in a covalently bondednetwork, as shown in the example network 31 in FIG. 2 . In one furtherexample, the silicon oxycarbide particles 28 have an average maximumdimension of 1-75 micrometers. In one additional example, an averagemaximum dimension of the BMAS particles 30 is less than the averagemaximum dimension of the silicon oxycarbide particles 28.

The network 31 is amorphous and thus does not have long rangecrystalline structure. The illustrated network 31 is merely one examplein which at least a portion of the silicon atoms are bonded to both Oatoms and C atoms. As can be appreciated, the bonding of the network 31will vary depending upon the atomic ratios of the Si, C, and O. In oneexample, the silicon oxycarbide particles 28 have a compositionSiO_(x)M_(z)C_(y), where M is at least one metal, x<2, y>0, z<1, and xand z are non-zero. The metal can include aluminum, boron, transitionmetals, refractory metals, rare earth metals, alkaline earth metals orcombinations thereof.

In one example, the composite material 22 includes, by volume, 1-30% ofthe BMAS particles 30. In a further example, the composite material 22includes, by volume, 30-94% of the silicon oxycarbide particles 28. Inone further example, the composite material 22 includes, by volume,5-40% of the matrix 26 of silicon dioxide. In a further example, thecomposite material 22 includes, by volume, 1-30% of the BMAS particles30, 5-40% of the matrix 26 of silicon dioxide, and a balance of thesilicon oxycarbide particles 28. In any of the above examples, thecomposite material 22 can include, by volume, 1-5% of the BMAS particles30.

The barrier layer protects the underlying substrate 24 from oxygen andmoisture. For example, the substrate 24 can be a ceramic-basedsubstrate, such as a silicon-containing ceramic material. One example issilicon carbide. The silicon oxycarbide particles 28 and the BMASparticles 30 of the barrier layer function as an oxygen and moisturediffusion barrier to limit the exposure of the underlying substrate 24to oxygen and/or moisture from the surrounding environment. Withoutbeing bound by any particular theory, the BMAS particles 30 enhanceoxidation and moisture protection by diffusing to the outer surface ofthe barrier layer opposite of the substrate 24 and forming a sealinglayer that seals the underlying substrate 24 from oxygen/moistureexposure. Additionally, the cationic metal species of the BMAS particles30 (barium, magnesium, and aluminum) can diffuse into the siliconoxycarbide particles 28 to enhance oxidation stability of the siliconoxycarbide material.

FIG. 3 shows another example article 120 that includes the compositematerial 22 as a barrier layer arranged on the substrate 24. In thisexample, the article 120 additionally includes a ceramic-based top coat132 interfaced with the barrier layer. As an example, the ceramic-basedtop coat 132 can include one or more layers of an oxide-based material.The oxide-based material can be yttria stabilized zirconia, gadoliniastabilized zirconia, or combinations thereof, but is not limited to suchoxides.

FIG. 4 illustrates another example article 220 that is somewhat similarto the article 120 shown in FIG. 3 but includes a distinct intermediatelayer 234 interposed between the barrier layer of the composite material22 and the substrate 24. In this example, the distinct intermediatelayer 234 includes an intermediate layer matrix of silicon dioxide 236and a dispersion of intermediate layer silicon oxycarbide particles 238in the intermediate layer matrix 236. The intermediate layer siliconoxycarbide particles 238 are similar to the silicon oxycarbide particles28 in composition but, in this example, the intermediate layer siliconoxycarbide particles 238 have an average maximum dimension (D2) that isless than the average maximum dimension (D1) of the silicon oxycarbideparticles 28. The relatively small intermediate layer silicon oxycarbideparticles 238 provide a relatively low roughness for enhanced bondingwith the underlying substrate 24. The larger silicon oxycarbideparticles 28 of the barrier layer provide enhanced blocking ofoxygen/moisture diffusion. Thus, in combination, the barrier layer andintermediate layer 234 provide good adhesion and good oxidation/moistureresistance. In one further example, D1 is 44-75 micrometers and D2 is1-44 micrometers.

In one example, the intermediate layer 234 can include, by volume, 5-40%of the intermediate layer matrix of silicon dioxide 236 and a balance ofthe intermediate layer silicon oxycarbide particles 238. In furtherexamples, a portion of the BMAS particles 30 from the barrier layer canpenetrate or diffuse into the intermediate layer 234, during processing,during operation at high temperatures, or both. In a further example, aseal coat layer of SiO₂, with or without BMAS particles, can be providedbetween the barrier layer and the intermediate layer 234 to providedadhesion and additional sealing. In further examples of any of thecompositions disclosed herein, said compositions can include only thelisted constituents. Additionally, in any of the examples disclosedherein, the matrix 26 and 236 can be continuous. The two-layer structurecan also demonstrate good oxidation protection at 2000-2700° F. for 500hours or longer as well as good adhesion with the ceramic-based top coat132.

The barrier layer and/or intermediate layer 234 can be fabricated usinga slurry coating method. The appropriate slurries can be prepared bymixing components, such as silicon oxycarbide, barium-magnesiumalumino-silicate, and powder of silicon dioxide or colloidal silica(Ludox) in a carrier fluid, such as water. The slurries can be mixed byagitation or ball milling and the resulting slurry can be painted,dipped, sprayed or otherwise deposited onto the underlying substrate 24.The slurry can then be dried at room temperature or at an elevatedtemperature to remove the carrier fluid. In one example, the slurry isdried and cured at about 200° C. for at least 15 minutes to ensureproper cross-linking of the coating. The green coating can then besintered at an elevated temperature in air for a selected amount oftime. In one example, the sintering includes heating at 1500° C. orgreater in an air environment for at least 1 hour.

The bond coat can be prepared using a slurry coating method. Slurriescan be prepared by mixing components such as SiOC, BMAS, SiO₂ or Ludox(a source colloidal SiO₂) and water using agitation or ball milling.Various slurry coating methods such as painting, dipping and sprayingcan be used to coat ceramic matrix composite (CMC) substrates. Coatingsformed from slurry are dried at room temperature and cured at 200° C.for at least 15 minutes. This curing step is critical to ensure propercross-linking of the coating. Failure to do so will result in coatingdamage during coating of subsequent layers. This coating process can berepeated until all layers are coated. The bond coat is finally sinteredat 1500° C. in air for 1 hour.

In one further example, a slurry of SiOC/SiO₂ 75/25 vol % was preparedby mixing appropriate amounts of SiOC and Ludox AS 40 colloidal silica.A small amount of water was added to adjust the viscosity. The slurrywas further mixed by ball milling for at least 15 hours. A slurry ofSiOC/BMAS/SiO₂ 80/5/15 vol % was prepared likewise by mixing appropriateamounts of SiOC, BMAS and Ludox AS 40 colloidal silica and ball millingfor more than 15 hours.

An inner layer was applied on a cleaned CMC substrate by painting. Thecoating was then dried at room temperature for 15-20 minutes until thepainted coating was completely dry and heated in oven at 200° C. for atleast 15 minutes to ensure complete cross-linking of the colloidalsilica. Incomplete cross-linking could result in coating cracking orre-dispersion of the particles in subsequent processing steps. An outerlayer was applied in the same fashion as the inner layer with theexception that the outer layer was applied with two passes. In betweenthe two passes, a silica sealing layer was coated to reduce the porosityin the outer layer. This silica sealing layer was prepared by submergingthe specimen in 50 wt % Ludox AS 40 colloidal silica solution, airdrying at room temperature and cross-linking at 200° C. This sealinglayer also effectively increased the overall SiO₂ content in thecoating. After completion of the two layer bond coat, the specimen wassintered at 1500° C. for 1 hour in air.

Although a combination of features is shown in the illustrated examples,not all of them need to be combined to realize the benefits of variousembodiments of this disclosure. In other words, a system designedaccording to an embodiment of this disclosure will not necessarilyinclude all of the features shown in any one of the Figures or all ofthe portions schematically shown in the Figures. Moreover, selectedfeatures of one example embodiment may be combined with selectedfeatures of other example embodiments.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed examples may becomeapparent to those skilled in the art that do not necessarily depart fromthe essence of this disclosure. The scope of legal protection given tothis disclosure can only be determined by studying the following claims.

The invention claimed is:
 1. A composite material comprising: a matrixof barium-magnesium alumino-silicate or SiO₂; a dispersion of siliconoxycarbide particles in the matrix, the silicon oxycarbide particleshaving Si, O, and C in a covalently bonded network; and a dispersion ofparticles, of the other of barium-magnesium alumino-silicate or SiO₂, inthe matrix, wherein the composite material forms a layer having a firstside and a second side, and wherein barium-magnesium alumino-silicateparticles are concentrated near the first side, thereby forming asealing layer.
 2. The composite material as recited in claim 1,including, by volume, 1-30% of the barium-magnesium alumino-silicateparticles, 5-40% of the matrix of SiO₂, and a balance of the siliconoxycarbide particles.
 3. The composite material as recited in claim 2,including, by volume, 1-5% of the barium-magnesium alumino-silicateparticles.
 4. The composite material as recited in claim 1, wherein thematrix of SiO₂ is continuous.
 5. The composite material as recited inclaim 1, including, by volume, 30-94% of the silicon oxycarbideparticles, 5-40% of the matrix of SiO₂, and 1-5% of the barium-magnesiumalumino-silicate particles.
 6. The material of claim 1, wherein thesilicon oxycarbide particles have a composition SiO_(x)M_(z)C_(y), whereM is at least one metal, x<2, y>0, z<1, and x and z are non-zero.
 7. Thematerial of claim 1, wherein the second side of the layer is adjacent asubstrate.
 8. The material of claim 1, wherein a cationic metal speciesfrom the barium-magnesium alumino-silicate particles is diffused intothe silicon oxycarbide particles.
 9. The material of claim 1, wherein anaverage maximum dimension of the silicon oxycarbide particles is between1 and 75 micrometers.
 10. The material of claim 9, wherein an averagemaximum dimension of the silicon oxycarbide particles is between 44 and75 micrometers.
 11. A composite material comprising: a matrix ofbarium-magnesium alumino-silicate or SiO₂; a dispersion of siliconoxycarbide particles in the matrix, the silicon oxycarbide particleshaving Si, O, and C in a covalently bonded network; and a dispersion ofparticles, of the other of barium-magnesium alumino-silicate or SiO₂, inthe matrix, wherein the composite material includes, by volume, 30-94%of the silicon oxycarbide particles, 5-40% of the matrix of SiO₂, and1-5% of the barium-magnesium alumino-silicate particles.